Atom:1.An atom is the smallest particle of an element that can take part in a chemical reaction.2.An atom may or may not exist independently.
3.Examples: hydrogen (H), oxygen (O).
Molecule:
1.A molecule is the smallest particle of an element or compound which has the properties of that element or compound.
2.A molecule is capable of independent existence.
3.Examples: hydrogen molecule , oxygen molecule , water molecule .